1. Field of the Invention
The present invention relates to a silver halide photographic light-sensitive material which contains a silver halide emulsion layer having an improved spectral sensitizing action, and, more particularly, it is concerned with a silver halide photographic light-sensitive material (wherein certain couplers may be incorporated or not) made up of at least two silver halide emulsion layers including a red-sensitive silver halide emulsion layer. Another layer may be another red-sensitive silver halide emulsion layer, a blue-sensitive silver halide emulsion layer or a green-sensitive silver halide emulsion layer.
2. Description of the Prior Art
It is well known in the art of sensitive material making that a silver halide photographic light-sensitive material, especially a color sensitive material, has a multilayer structure comprising at least one red-sensitive emulsion layer, at least another photosensitive emulsion layer, an interlayer and other layers. In such a case, spectral sensitization techniques (i.e., techniques of enlarging the wavelength region of radiation sensitivity which a silver halide photographic emulsion inherently possesses, by adding certain sensitizing dyes thereto) have been commonly applied in order to provide blue sensitivity, green sensitivity and red sensitivity to the respect photosensitive emulsion layers.
The spectral sensitizing powder depends upon the chemical structure of a spectral sensitizing dye itself and the nature of the emulsion wherein said dye is incorporated (e.g., the composition of halogens constituting the silver halide grains incorporated therein, the crystal habit thereof, the silver ion concentration, the hydrogen ion concentration and so on). In addition, the spectral sensitivity achievable by taking advantage of spectral sensitization techniques can also be influenced by additives as are universally employed in the photographic art, such as a stabilizer, an anti-foggant, a coating assistant, a color coupler and so on, which are present in the emulsion to which a sensitizing dye is added. Examples of conventionally used sensitizing dyes which can provide red sensitivity to the emulsion layer containing them include, for example, quinoline nucleus-containing carbocyanine dyes as are disclosed in U.S. Pat. No. 3,556,800; rhodacyanine dyes as are disclosed in Japanese Patent Publication 4,930/68; merocyanine dyes as are disclosed in U.S. Pat. No. 3,416,927; dicarbocyanine dyes as are disclosed in U.S. Pat. Nos. 2,503,776 and 3,635,721, Japanese Patent Publication 550/71 and Hamer, The Cyanine Dyes and Related Compounds, p. 207 (1964), published by Interscience Publication; and so on.
However, the fact that the addition of these sensitizing dyes to a silver halide emulsion produces side effects undesirable from a photographic point of view is also well known. The most undesirable of the above described side effects in the production of multilayer silver halide color photographic materials of high spectral sensitivity are a deterioration phenomenon which increases with the passage of time (spectral sensitivity tends to deteriorate with the passage of time) and a diffusion sensitization action (the phenomenon that some portion of the sensitizing dye added to a certain emulsion layer diffuses into other layers with the passage of time without remaining where it was added, and exert an undesirable sensitization effect in the final layer into which they diffuse; such a phenomenon is termed "diffusion sensitization" hereinafter).
In particular, diffusion sensitization has a very bad effect on photographic properties because sensitizing dyes added to a red-sensitive emulsion layer diffuse into a green-sensitive and/or a blue-sensitive emulsion layer to result in panchromatic sensitization, which is responsible for color mixing (muddiness) in developed color images, for the decreased green sensitivity of the green-sensitive layer and/or the decreased blue sensitivity of the blue-sensitive layer.
Therefore, research and development of sensitizing dyes which cause little diffusion sensitization have been an important subject in this art.
Dicarbocyanine sensitizing dyes (containing a pentamethine chain therein) are, in general, superior to conventional sensitizing dyes employed for providing red sensitivity to a silver halide emulsion such as a 4-quinoline nucleus-containing carbocyanine dye (having a trimethine chain), a tetramethinemerocyanine dye and a rhodacyanine dye at various points, for example, from the viewpoint of keeping spectral sensitivity in a sensitive material, of keeping sensitivity upon dissolution in the emulsion before it is coated, solubility, sensitizing properties, printing aptitude and temperature dependence, but they have the difficulties that their spectral sensitivity is substantially reduced with the passage of time and they result in an appreciable diffusion sensitization under conditions of high humidity.
Accordingly, it is actually difficult to use commonly known dicarbocyanine dyes as they are (independently) without overcoming the above described difficulties. However, it has been believed that dyes of this kind would be very useful dyes capable of providing red sensitivity to a silver halide photographic emulsion if the above described difficulties could be overcome.